Black spot causes large irregular black spots on both sides of the leaves. The spots have concentric zonations and often run together. Many leaves yellow and die prematurely. In spring there may be black, canker-like spots on the leaves, stems and flower stalks. The stems shrivel at the point of infection and fall over. The leaves and unopened flower buds wilt. The flowers may also have black spots. Remove infected leaves and flowers. The causal organism is Coniothyrium hellebori and there is no chemical control.
Blight and crown rot caused by Botrytis cinerea may be controlled with sprays of benomyl.